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Unrrn Smarts Parent HUBERT HENRY GRUBBE, OF LONDON, ENGLAND, ASSIGNOR OFONE-HALF TO CHARLES HORACE BENTON, OF SAME PLACE.

PROCESS OF MAKING INCANDESCENTS.

SPECIFICATION forming part of Letters Patent. No. 323,319, dated July28, 1885.

Application filed December 12. 1883. (No specimens.)

Carbon filaments for incandescent lamps have been heretofore made bothfrom inor-- ganic snbstances-as retort -carbon, carbon deposited from ahydrocarbon vapor on a heated conductor, and the like-and by carbonizingorganic or structural substances. The organic substances may be dividedinto two classes-those ofa fibrous character, or wherein the originalorganic structure is preserved, and those of a non-fibrous orhomogeneous character, or in which the original organic structure isdestroyed by chemical treatment. lVith both classes of organicsubstances it has been customary to employ to a greater or less extentthe process of parch1nentizingthat is, the treatment of the organicsubstances with acid, usually sulphuric acid,which softens the celluloseand converts it into a substance which, on being dried, resemblesparchment.

In preparing the incandescing conductor of fibrous organic substances,various methods have been followed. According to one method, bibulouspaper has been parchmentized by dipping in sulphuric acid, and thenbeing cut into strips, carbonized by placing it in a closed refractoryvessel, covering it with carbonpowder or other oxygen-excluding powder,and subjecting it to an intense heat. Accord ing to another method,cotton thread has been used, which, after being dipped in acid, has .0been thickened at the clamping ends of the filament by wrapping themwith paper or thread, and then dipping these enlarged ends in the acid,and finally carbonizing as before. Substantially the same processes havebeen 5 followed with various other fibrous substances of vegetableorigin, among others wood, rattan, and certain vegetable fibers.

In preparing the incandesciug conductor of non-fibrous or homogeneousorganic substance, several different methods have been followed,

I ized.

mainly based upon the action of acids upon cellulose, whereby thevegetable structure or fiber is dissolved. By one method vegetable fiber(cellulose) is treated with nitric and sulphuric acids, formingnitro-cellulose. This is dissolved by nitro benzole, naphtha, orcamphor, forming celluloid, and this is deoxidized or deprived of itsnitrous elements, and thereby rendered a non-structural cellulose, whichis formed into sheets, from which sheets the (i0 filaments are out, andthe latter are then carbonized. Another method consists in pressing apasty mass of dissolved cellulose through a small orifice, therebyforming it into a slender filament which is subsequently carbonized. 6 5The enlarged ends on this filament are formed by softening the ends bydipping in a solvent and then molding to them pieces of cellulose.Sheets of dissolved cellulose, or compounds of which cellulose forms apart, have been dried and cut into filaments which have then beencarbonized, being sometimes first parchment- W'hen the sheets have beeninaccurate, it has been proposed to scrape them by pass ing them throughscraping or shaving dies.

My present invention relates to the processes of preparing theincandesci 11g conductor, wherein the fibrous or structural cellulose isemployed, the vegetable fiber remaining intact during the operation andexisting in the completed filament. My improved method is characterizedby the softening of the vegetable fibers, or of the portion thereofdestined to form the luminous filament by means of a suitable solvent,and then reducing and compact 8 ing the softened fibers by drawing thesame through a die or dies. The fibers so treated are then carbonized bythe usual baking process, and have carbon deposited on them in the usualmanner.

In carrying out my invention I employ, by preference, the fiber known asMexican fiber, but many other vegetable fibers will answer the purpose,as will be well understood. Iimmerse such portion of the length of thefiber as is required to form thefilament in some suitable solvent orsoftening liquid, in order to soften or partially dissolve the fibers. Iprefer an acid solution consisting of two parts of sulphuric acid to onepart of water, The duration of the immersion will vary according to thecharacter and strength of the solution and the character and thicknessof the fiber. The effect of this immersion is to dissolve away ordestroy a portion of the outer texture of the fiber and render it softand capable of being compressed or compacted. On removing the fiber fromthe solvent I wash it in water. I next proceed to draw the softenedfiber through dies, in order to compact it and reduce it to a uniformdiameter and density. It is best to grasp the fiber by those portions ofits length which have not beenimmersed in the solvent, and which aretherefore still hard, and, using "a divided die, place the fiber in thedie, bring the opposite portions thereof together, confining the fiberbetween the1n,and then draw the fiber through the die after the mannerof wire drawing. The action of the die is to compress and compact theportion of the fiber which has been softened by the acid solution,removing any irregularities that may exist. If neces sary, two or moredies of different gages may be employed, the fiber being passed throughthem successively, the smallest die corresponding to the diameterrequired in the filament.

The fiber thus prepared is very dense and very uniform in texture anddiameter. It is completed to form the filament by baking or carbonizingin the well-known manner, and then, by preference, has a deposit ofcarbon formed upon itby being heated in a hydrocarbon vapor. Thefinished filament is dense, tough, and elastic, retains the fibrousstructure of the fiber from which it was made, and possesses a uniformelectric conductivity and a high specific resistance, the particularresistance desired being readily obtained by the use of a larger orsmaller die for the final drawing.

it will be observed that in using sulphuric acid for softening the fiberthe outer or surface portion of the cellulose constituting the vegetablefiber is parchmentized; but this result,whi1e advantageous, is notessential to my invention, as any solvent or softening substance orsolution may be used which will act sufiiciently upon the harsher outerportions of the fiber and soften the same preparatory to drawing throughdies without so weakening or injuring the fibrous structure as to causeit to give way during the drawingoperation.

My method of drawing a softened vegetable fiber through dies is to beclearly distinguished from the method of forcing a pasty mass ofunstructural cellulose through a small perforation, whereby it ispressed out into a slender thread, substantially as in makingvermicelli. It is also to be distinguished from another method which hasbeen proposed in the manufacture of incandescing filaments, and whichconsists in the drawing of fibers (not previously softened) through around hole, in order to removefrom them a superfluity of oil andlamp-black, with which they have been coated.

I make no claimto a flexible carbon filament formed of carbonizedparchmentized cellulose; nor do I claim the method of forming such afilament by carbonizing parchmentized cellulose and reducing thematerial to the proper size and shape, as these features were knownprior to my invention; but

What I do claim, and desire to secure by Letters Patent, is-

1. The improved method of preparing carbon filaments for incandescentelectric lamps, which consists in softening vegetable fibers byimmersing in a solvent liquid, then drawing the softened fiber through adie or dies until reduced to the desired diameter, and then carbonizingthe same, substantially as specified.

2. The improved method of preparing carbon filaments for incandescentelectric lamps, which consists in softening vegetable fibers byimmersing in a solvent liquid, then drawing the softened fiber through asuccession of dies until reduced to the desired diameter, thencarbonizing the same, and finally depositing carbon thereon,substantially as set forth.

In witness whereof I have hereunto signed my name in the presence of twosubscribing witnesses.

HUBERT II. GRUBBE.

\Vitnesses:

JOHN C. NEWBURN, GEORGE 0. Bacon.

